Preparation of 4, 5-dihydro-2-methylfuran



United States Patent 0.

REP R T O O 4, :DI Y Rr2- METHYL-FURAN Norman L. Hause, -;G raud :Islaud, :N. Y., assignor to .d 1 qnt 1 Nem qr ans ampa W a an, De acorporation of Delaware No Drawing. Application March 17, 1954, Serial No. 416,947

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This invention relates to thepreparation of,4,5- dih.y dro- Z-methylfuran by .the dehydration of acetopropanol acw diq t .t fi uafl m 2-hydroxy-2 methyl-tetrahydro furan This application is a continuation-in-part of copend- .i a pp ca o S ri N m e ,-699 fi d Feb u 20, 1952, now abandoned.

vsc m pp d 2 .1. A- as. 9. 672-. 7. ),.r.eported thepreparation of the above dihydromethylfuran ingood yields bythe. dehydrative distillation of vervsmall amounts of acetopropanol using a ,helices packed column. ,Ithasbeen found, however, that such arn thod gives highly erratic results, particularly when ,si able products. easily, occur. More0vcr,:whilelhave discovered h lh desired d h r on o a a r pan li catalyzed by the presence of angiacid, the reverse reaction, i e, th hy n o i yd -2:m th l a ,to a at propanol, also occurs very readily in the presence ;0 f an acid.

It is anobject of the invention to provide ,an improved method for the production of 4,5-dihydro-2-methylfuran from acetopropanol. A further object is to provide a more reliable method .of producing this dihydromethylfuran .by :the dehydrative distillation of acetopropanol. Still further objects are the improvement of prior distillation methods and catalysts whereby consistently good conversions to the desired dihydromethylfuran' can be readily obtained. Other objects will be apparent-fromjhe following description. c

The above objects are accomplished in accordance-"with the invention by subjecting acetopropanol containing nonvolatile acid catalyst to distillation conditions While continuously adding further amounts of acetopropanol to the body of liquid undergoing distillation at such a rate as will maintain that body at a substantially constant volume. It has been found that prolonged heating of acetopropanol during distillation is highly disadvantageous in that it increases the extent to which side reactions occur. By continuously adding fresh acetopropanol to the still so 2,758,] 18 Rate i Aug 7, 1. .5

r 2 as to maint in the volume ofliquidjn the stilhsuhstantially c ns an du ng th d st lla n, th e d rin which a unit amount of .matcrial is held atthe te pertitures v necessary for distillation is minimized, thus reducing the conversion of acetopropanol ;-to undesired Jayproducts.

The volume of liquid to bemaintainedi-n the ,still pot during distillation maybevaried considerably andusually will vary with the scale of operation, -but ;should;-a lways be small compared with thetotal volume ofthe material to be distilled. Generally, the volume ofliquid in the still to which-further amounts of acetopropanol areadd ed as distillation proceeds willnot-exceed; about 305% j-of the total volume of acetopropanol which is ;to be distilled; pr e y, it .will be ss t a 2. a [on h ord. o 1 5%- en p oduc i is o e i I erally be less than 1%.of,the volume to be distilled over a time unit of several hours. The rate of addition of acetopropanol. duringthe distillation will approximate, the rate atwhich dihydromethylfuranland .water are distilled fiorn the system.

Best results :arebbtjained employing a distillation pot provided -with an unpacked .columnthrough which the vapors of .dihydromethylfuran and water .are passed it) the condenser. iIt has been found that useof an unpacked "fractionating column is distinctly advantageous "fromthe conversionstandpoint. over the .--use of a packed column. Preferably. the unpacked column willlbe jacketed and heated, e. g., to a temperature-in the :range :of 530 to :C. for most operations, andflwill have-azlength which. isabout l0."'70,.most preferably .about1 2-5140, times its diameter, 580 .as to avoidexcessive hold up of vap.o rs in. the colummwhile providing elfective condensationand return zofacetopropanol tothelstill pot.

Dehydrat'ive .-disti'l lation.of zpure :acetopropanOL-to 4,5- dihydro-2 methylfuran cannot be effected. Traceamounts of acid will catalyzethereaction. Largeamounts .of; acid willcause. excessive polymerizationofithe. stillpot charge. Therefore the amount of acid to be used as catalyst is highly critical. The use. of-.volatile acids is undesirable sinc e vapors of volatile K acids catalyze ,recombination of hy rom .th .u an .wateri th olum n othe parts of. the. distillation system. Theacidused should 9f som not b -9 hich re ad crs l itha c p anc zo z ihrdmm thylfi r n- Ihwcace t on o the non-volatile acidtshouldbebelow. about 0.5 .ohthe weight of the body of liquid in the still pot during distillation. Larger amounts cause excessive polymeriza- Qn--t -.QQ h rre red c ncsnt a i n a i nr Ians D-m-to 9,95%sbyw gh xamples s a le anwl ti id -a e pho phori -a i s lfu a id, --s. ear. av d :s d am flihy aa ,Ph SP EB and sod m hi s i t hausw nh sphoricasidai ,P eterre Ih @QIl d c th n ent o .u ually i os o .v a mly a ri ou at a ppressu a prqx m ia ama :P h Pres r al aa l h o ow res-sum ca be used. The use of higher pressures requires, .of course, that the acetopropanol and the vaporous products be subjected to higher temperatures, which generally is disadvantageous and results in greater conversion tchy-products.' While good conversions pan be realized at subatmospheri c pressures, e. g., as low -as around 1- 2 59 mm. Hg, the 'dehydration reaction occurs more slowly under sub-atmospheric conditions in view of the lower temperatures involved. However, because of such lower temperatures, packed fractionating columns can be used with less disadvantage than when operating at atmospheric or higher pressures.

It is generally advantageous and advisable to add a small amount of a base such as an alkali or alkaline earth metal carbonate or bicarbonate to the distillate receiver to neutralize any acidic material that may be prescut. The amount of base to be used for this purpose is not critical and generally will be on the order of about 1-2% of the weight of the distillate to be collected.

There is a tendency for a dihydromethylfuran-acetopropanol addition product to be formed in the body of liquid undergoing distillation. It has been discovered that this tendency can be reduced and the conversion to 4,5- dihydro-2-methylfuran correspondingly increased by adding a small amount of water along with the acetopropanol -to the body of liquid undergoing distillation, particularly towards the end of the distillation or when the rate of distillation decreases due to build up of such by-product in the still pot. Water so added appears to hydrolyze the by-product which has been formed and convert it back to acetopropanol which is then available for the desired dehydration reaction. An amount of water equal to about 1 to of the weight of the acetopropanol being distilled is generally eflective for this purpose, although larger or smaller amounts can be used with advantage.

The invention is illustrated by the following examples.

Example I About ml. of a solution of 4 ml. of 0.3 N phosphoric acid in 300 g. (2.94 moles) of acetopropanol was placed in a 200 ml. three-necked flask set for distillation through a 1.5 x 45 cm. jacketed heated Vigreux column, the latter being preheated to C. by means of an electrically heated jacket. When the temperature of the flask contents reached 175 C., the dehydration reaction began. The remainder of the acetopropanol-phosphoric acid solution was fed into the flask at approximately the rate at which the dihydromethylfuran and water were distilled at the column head so that the volume of liquid in the flask remained substantially constant. The head temperature remained between -97 C., while the temperature of the liquid in the flask rose slowly during the distillation from C. to C. After all of the acetopropanol solution (300 g.) had been added, the temperature of the residue in the flask climbed gradually to 260 C. A total of 212 g. of 4,5-dihydro-2-methylfuran, representing an 85% conversion, was collected during the four hour distillation period. About 26 g. of residue remained in the flask.

Example 2 Three hundred grams (2.94 moles) of acetopropanol containing 3 ml. of 0.3 N phosphoric acid, was distilled as described in Example 1 except that the material was all placed in the distillation flask at the start. In this case, the conversion to 4,5-dihydro-2-rnethylfuran was only 56% and the still residue was 86 g.

Example 3 Sixty g. (0.59 mole) of acetopropanol containing 0.75 ml. of 0.3 N phosphoric acid was distilled from a flask set for distillation through an asbestos-wrapped column having a 2.5 x 37 cm. section packed with berl saddles. No yield of 4,5-dihydro-2-methylfuran was obtained during a four hour period and substantially all of the material added remained in the flask as resinous or high boiling by-products, including perhaps some unconverted acetopropanol.

Example 4 The experiment of Example 3 was repeated except that the berl saddles were removed from the column. In this case, the amount of 4,5 -dihydro-2-methylfuran obtained as distillate corresponded to a conversion of 65%.

Example 5 Five milliliters of 0.3 N prosphoric acid was added to 240 g. (2.37 moles) of acetopropanol and 50 ml. of the resulting solution was placed in a 500 ml. three-necked flask equipped with a thermometer and an addition funnel and set for distillation through a vacuum-jacketed, silver-lined column having a 1 x 36-inch section packed with protruded metal packing. The material was distilled through this column at a pressure of 4-15 mm. Hg. Small portions of the acetopropanol-phosphoric acid solution were added as distillation proceeded so as to keep the volume of liquid in the flask substantially constant. After all of the acetopropanol had been added, small portions of water (about 1% by weight of the flask contents) were added so that the residue in the flask was kept boiling vigorously. After thirteen hours of distillation, 166 g. of 4,5-dihydro-2-methylfuran, corresponding to a conversion of 84%, had been collected in the cooled receiver. The residue in the distillation flask was 31 g.

4,5-dihydro-2-methylfuran is useful as a chemical intermediate. Thus, it can be chlorinated to produce 2,3- dichlorotetrahydro-2-methylfuran in good yield as disclosed in my application S. N. 272,700, filed February 20, 1952, now Patent No. 2,678,319. This dichloro compound can then be reacted with thioformamide to obtain 4-methyl-S-(fl-hydroxyethyl)-thiazole as disclosed in U. S. P. 2,654,760 Londergan and Schmitz, issued October 6, 1953. The resulting thiazole is an important vitamin B1 intermediate.

Wherever the term acetopropanol is used in this specification the compound is the same as gamma acetopropanol.

I claim:

1. The method of preparing 4,5-dihydro-2-methylfuran comprising distilling gamma acetopropanol containing a catalytically effective amount of a non-volatile acid selected from the group consisting of phosphoric acid, sulfuric acid, stearic acid, sodium hydrogen phosphate and sodium bisulfate, and collecting 4,5-dihydro-2-methylfuran and water as distillate while adding gamma acetopropanol to the body of liquid gamma acetopropanol undergoing distillation at such a rate that said body is maintained at a substantially constant volume during the course of the distillation.

2. The method of claim 1, wherein the gamma acetopropanol undergoing distillation contains a non-volatile acid in an amount not exceeding 0.5% by weight.

3. The method of claim 2, wherein the non-volatile acid content of the gamma acetopropanol undering distillation is within the range 0.01 to 0.05% by weight.

4. The method of claim 1, wherein the gamma acetopropanol fed to the liquid undergoing distillation contains a small amount of water, said water constituting between about 1% and 30% by Weight of said liquid undergoing distillation.

Lipp: Berichte, vol. 22, pp. 1196-1205 (1899).

Schniepp et al.: J. A. C. S., 69, pp. 672-74 (1947).

Wohlgemuth: Annales de Chemie (9), 2, pp. 425-8 (1914) 

1. THE METHOD OF PREPARING 4,5-DIHYDRO-2-METHYLFURAN COMPRISING DISTILLING GAMMA ACETOPROPHANOL CONTAINING A CATALYTICALLY EFFECTIVE AMOUNT OF A NON-VOLATILE ACID SELECTED FROM THE GROUP CONSISTING OF PHOSPHORIC ACID, SULFURIC ACID, STEARIC ACID, SODIUM HYFROGEN PHOSPHATE AND SODIUM BISULFATE, AND COLLECTING 4,5-DIHYDRO-2-METHYLFURAN AND WATER AS DISTILLATE WHILE ADDING GAMMA ACETOPROPANOL TO THE BODY OF LIQUID GAMMA ACETOPROPANOL UNDERGOING DISTILLATION AT SUCH A RATE THAT SAID BODY IS MAINTAINED AT A SUBSTANTIALLY CONTANT VOLUME DURING THE COURSE OF THE DISTILLATION. 